Visual display units, (flat) screens, displays, television sets and monitors with high resolution comprise an electrical connection interface, in particular in form of a DVI data transmitting interface and/or HDMI data transmitting interface. In addition to various control signals, several differential TMDS encoded signals for the transmission of audio and video data as well as the required clock signal between at least one data source and at least one data sink are carried via this interface.
In this connection, TMDS (=Transition-Minimized Differential Signaling) is basically a digital transmission standard for uncompressed multimedia data, having been developed to eliminate electromagnetic disturbances occurring at analogue transmission; in this way, TMDS is used for instance at DVI transmissions (DVI=Digital Visual Interface) and/or at HDMI transmissions (HDMI=High Definition Multimedia Interface) in order to control screens with very high resolution, wherein TMDS encoded signals may comprise data rates in the region of several gigabits per second.
According to page 38 of version 1.3a of the HDMI specification dated 10 Nov. 2006 (participating companies: Hitachi Ltd., Matsushita Electric Industrial Co. Ltd., Philips Consumer Electronics International B.V., Silicon Image Inc., Sony Corporation, Thomson Inc., Toshiba Corporation), the TMDS technology uses a current driver in order to generate a differential low voltage signal on the sink side of a direct current coupled transmission line.
The termination voltage or supply voltage defines the upper voltage value for each of both terminals of the differential signal whereas the lower voltage value is determined by the current source of the HDMI source and by the terminating resistor at the sink. The terminating resistor and the characteristic impedance of the cable are to be adapted to each other.
In detail, the electrical connection is effected between the connection interface of the data source and the connection interface of the data sink, for example by means of a copper cable KK (with impedance Z0 per differential pair of copper wires; cf. FIG. 3). The TMDS encoded signals are provided as output current signal from the data source by means of an output current driver (transmitter TM with current source SQ and changeover switch D, D′; cf. FIG. 3).
The correct line termination in the receiver (receiver RC; cf. FIG. 3) is effected by the direct voltage coupled transmission channel KK between the data source and the data sink. At this line termination in form of two ohmic resistors RT, RT′ connected in parallel (cf. FIG. 3) in the receiver RC, the input signal voltage necessary for the input amplifier EV is generated with reference to the supply voltage AVCC.
FIG. 3 shows the above-described with regard to the prior art in form of a conceptual schematic circuit diagram for a differential TMDS signal wherein it can be further taken from FIG. 3 that the receiver RC adopts the direct voltage supply of the output current driver of the transmitter TM. In addition, the connection interface of the data source provides a voltage supply in the order of about five volt for the data sink, wherein said voltage supply may be loaded with not more than about 55 milliampere.
As to the depicted prior art, it has to be considered that TMDS encoded signals of an HDMI data connection are to be able to support data transmission rates of several gigabits per second and per differential pair of wires AD, AD′ (cf. FIG. 3) of the copper cable KK. This involves that highest-quality and thus expensive copper cables are to be used in case of longer distances between data source and data sink.